Inflight entertainment system network configurations

ABSTRACT

Serial networking dedicated fiber optic inflight entertainment (IFE) systems, methods therefor and components thereof, that exhibit improved configuration and failover attributes through implementation of novel network configuration protocols. In some aspects of the invention, such an IFE system comprises a plurality of head end line replaceable units (HE-LRUs) and a plurality of serial networking line replaceable units (SN-LRUs), wherein each of the SN-LRUs individually detects that a closed system network has been formed between the plurality of HE-LRUs and the plurality of SN-LRUs based on a plurality of packets sourced by at least one of the HE-LRUs and received on a plurality of ports of each of the SN-LRUs, and wherein in response to detecting that the closed system network has been formed one of the SN-LRUs blocks one of its ports based on further detecting that the SN-LRU is a middle SN-LRU.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/685,525, entitled “SERIAL NETWORKING FIBER OPTIC INFLIGHTENTERTAINMENT SYSTEM NETWORK CONFIGURATION”, filed on Nov. 26, 2012, nowU.S. Pat. No. 9,036,487, which is a continuation of U.S. applicationSer. No. 12/860,437, entitled “SERIAL NETWORKING FIBER OPTIC INFLIGHTENTERTAINMENT SYSTEM NETWORK CONFIGURATION,” filed on Aug. 20, 2010, nowU.S. Pat. No. 8,416,698, which claims priority from U.S. provisionalapplication No. 61/274,726 entitled “SERIAL NETWORKING FIBER-TO-THE-SEATINFLIGHT ENTERTAINMENT SYSTEM NETWORK MANAGEMENT,” filed on Aug. 20,2009, the entirety of each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Inflight entertainment (IFE) systems have evolved significantly over thelast 25 years. Prior to 1978, IFE systems consisted of audio-onlysystems. In 1978, Bell and Howell (Avicom Division) introduced a groupviewing video system based on VHS tapes. In 1988, Airvision introducedthe first inseat video system allowing passengers to choose betweenseveral channels of broadcast video. In 1997, Swissair installed thefirst interactive video on demand (VOD) system. Currently, several IFEsystems provide VOD with full digital video disc-like controls.

The commercial viability of an IFE system generally depends on its linereplaceable units (LRUs). The term “LRU” is a term of art generallydescribing a complex component (e.g. “black box”) on an airplane that isdesigned to be replaced quickly on the flight line or airport ramp area.LRUs can be beneficial because they are generally self-contained unitsthat can be rapidly swapped-out in the event that maintenance isrequired thus allowing the airplane to continue to operate with littledown time. Before being installed on an airplane, an LRU design shouldbe approved by the Federal Aviation Administration by means defined inTitle 14 of the Code of Federal Regulations. An IFE system'sinstallation costs, operating costs, maintenance costs and passengercomfort depend greatly on the size, form factor, number and weight ofits LRUs, as well as the number of distinct LRUs deployed in a singleaircraft and across an airline's entire fleet of aircraft.

SUMMARY OF THE INVENTION

The dedicated fiber optic IFE system architecture described in U.S.Patent Application Publication No. 2007/0077998, for example the systemmarketed under the tradename FIBER-TO-THE-SCREEN™ (FTTS™) by Lumexis,Inc., has provided the airline industry with a modular, scalable,extensible, and future proofed IFE system that leverages terrestrial VODhardware and software advances and is packaged to minimize the number ofdistinct LRU not only in a single aircraft but across an airline'sentire fleet of aircraft (e.g. regional jets to jumbo jets). In somededicated fiber optic IFE systems, such as the system shown in FIG. 1,head end servers are interconnected in a ring using bidirectional fiberoptic links and communicate with passenger seat video display units(VDUs) over respective bidirectional links. This architecture offersadvantages over traditional IFE systems in eliminating distribution areaLRUs (i.e. there are no active components between the head end and theseat end). However, this architecture has certain drawbacks. First, ahead end server is single point of failure for all passenger seat VDUsand cabin management terminals that connect directly to that head endserver. Second, the implementation of a star wired network topologywherein each passenger seat VDU has a dedicated optical fiber “home run”to a head end server adds cost and complexity to the system. Forexample, over two miles of fiber are required on a typical narrow bodyaircraft installation and over four miles of fiber are required on atypical wide body aircraft installation. The high cost of aircraft gradefiber and fiber optic connectors, coupled with the cost and complexityof installing these fiber components, make this architecture veryexpensive to implement.

This architecture can be enhanced as generalized in FIG. 2, whereinreliability can be improved and costs reduced by providing a serialnetworking dedicated fiber optic IFE system wherein “chains” ofpassenger seat VDUs are connected on both ends to a “ring” of head endservers. In this enhanced architecture, rather than communicating withthe head end over a dedicated data path, each passenger seat VDUcommunicates with the head end over a shared loop-free data path of aserial network established on selected redundant physical connections.This architecture reduces fiber component requirements relative to thearchitecture generalized in FIG. 1 and has the potential to exhibitsuperior failure recovery characteristics. However, known networkconfiguration protocols that create loop-free network topologies, suchas Rapid Spanning Tree Protocol (IEEE Std. 802.1w), are not well-suitedfor use in serial networking dedicated fiber optic IFE systems.

Accordingly, in some embodiments, the present invention provides serialnetworking dedicated fiber optic IFE systems, methods therefor andcomponents thereof, that exhibit improved configuration and failoverattributes through implementation of novel network configurationprotocols. In various aspects of the invention, head end LRUs (HE-LRUs)may be head end servers of an IFE system and serial networking LRUs(SN-LRUs) may be passenger seat VDUs of an IFE system, by way ofexample.

In some aspects of the invention, an IFE system comprises a plurality ofHE-LRUs and a plurality of SN-LRUs, wherein each of the SN-LRUsindividually detects that a closed system network has been formedbetween the plurality of HE-LRUs and the plurality of SN-LRUs based on aplurality of packets sourced by at least one of the HE-LRUs and receivedon a plurality of ports of each of the SN-LRUs, and wherein in responseto detecting that the closed system network has been formed at least oneof the SN-LRUs blocks at least one of its ports based on furtherdetecting that the SN-LRU is a middle SN-LRU. The SN-LRU may determinethat it is a middle SN-LRU based on a comparison of hops to head endvalues contained in the plurality of packets. The SN-LRU may determinethat it is a middle SN-LRU based on the comparison indicating adifference between the hops to head end values of no greater than one.The SN-LRU may clear a topology database on the SN-LRU in response todetecting that the closed system network has been formed and based onfurther detecting that the SN-LRU is a middle SN-LRU. The SN-LRU maytransmit a topology change packet on an unblocked at least one of itsports in response to detecting that the closed system network has beenformed and based on further detecting that the SN-LRU is a middleSN-LRU. Moreover, each of the HE-LRUs may individually detect that aclosed head end network has been formed between the plurality of HE-LRUsbased on a packet transmitted by the HE-LRU on a first port and receivedby the HE-LRU on a second port, wherein in response to detecting thatthe closed head end network has been formed at least one of the HE-LRUsblock at least one of the first or second port based on furtherdetecting that the HE-LRU is a designated break LRU. The HE-LRU mayclear a topology database on the HE-LRU in response to detecting thatthe closed head end network has been formed and based on furtherdetecting that the HE-LRU is a designated break LRU. The HE-LRU maytransmit a topology change packet on an unblocked at least one of itsports in response to detecting that the closed head end network has beenformed and based on further detecting that the HE-LRU is a designatedbreak LRU.

In other aspects of the invention, a SN-LRU for an IFE system having aplurality of HE-LRUs and a plurality of SN-LRU comprises a processor anda plurality of ports communicatively coupled with the processor, whereinunder control of the processor the SN-LRU selectively blocks at leastone of the ports based on a comparison of a first hops to head end valuecontained in a first packet sourced by a HE-LRU and received on a firstone of the ports and a second hops to head end value contained in asecond packet sourced by a HE-LRU and received on a second one of theports. The SN-LRU may under control of the processor block at least oneof the ports if the comparison indicates that a difference between thehops to head end values is no greater than one. The SN-LRU may undercontrol of the processor block at least one port over which the packetcontaining the higher hops to head end value was received. The SN-LRUmay under control of the processor selectively clear a topology databaseon the SN-LRU based on the comparison. The SN-LRU may under control ofthe processor selectively transmit a topology change packet on anunblocked at least one of the ports based on the comparison.

In yet other aspects of the invention, a HE-LRU for an IFE system havinga plurality of HE-LRUs and a plurality of SN-LRU comprises a processorand a plurality of ports communicatively coupled with the processor,wherein under control of the processor the HE-LRU blocks at least one ofthe ports based on detecting that a packet transmitted on a first one ofthe ports has been received on a second one of the ports and based onfurther detecting that the HE-LRU is a designated break LRU. The HE-LRUmay under control of the processor clear a topology database on theHE-LRU based on detecting that a packet transmitted on a first one ofthe ports has been received on a second one of the ports and based onfurther detecting that the HE-LRU is a designated break LRU. The HE-LRUmay under control of the processor transmit a topology change packet onat least one unblocked port based on detecting that a packet transmittedon a first one of the ports has been received on a second one of theports and based on further detecting that the HE-LRU is a designatedbreak LRU.

In yet other aspects of the invention, a network configuration methodperformed by a SN-LRU of an IFE system having a plurality of HE-LRUs anda plurality of SN-LRUs comprises the steps of receiving on a first portof the SN-LRU a first packet sourced by a HE-LRU and having a first hopsto head end value, receiving on a second port of the SN-LRU a secondpacket sourced by a HE-LRU and having a second hops to head end value,comparing the first and second hops to head end values, and selectivelyblocking at least one of the ports based on the comparison. The methodmay further comprise blocking at least one of the ports if thecomparison indicates that a difference between the first and second hopsto head end values is no greater than one. The method may furthercomprise blocking at least one of the ports over which the packetcontaining the higher hops to head end value was received. The methodmay further comprise selectively clearing a topology database on theSN-LRU based on the comparison. The method may further compriseselectively transmitting a topology change packet on an unblocked portbased on the comparison.

In yet other aspects of the invention, an IFE system comprises aplurality of HE-LRUs and a plurality of SN-LRUs, wherein each of theSN-LRUs individually detects that a closed system network has beenformed between the plurality of HE-LRUs and the plurality of SN-LRUsbased on a plurality of packets sourced by at least one of the HE-LRUsand received on a plurality of ports of each of the SN-LRUs, and whereinin response to detecting that the closed system network has been formedat least one of the SN-LRUs provides a logical break point for thenetwork based on historical break information.

In still other aspects of the invention, a network configuration methodperformed by a SN-LRU of an IFE system having a plurality of HE-LRUs anda plurality of SN-LRUs comprises the steps of receiving on a first portof the SN-LRU a first packet sourced by a first HE-LRU, receiving on asecond port of the SN-LRU a second packet sourced by a second HE-LRU,determining by the SN-LRU that a closed system network has been formedbetween the plurality of HE-LRUs based on the first and second packet,determining by the SN-LRU that the SN-LRU provides a logical break pointfor the network based on historical break information and providing bythe SN-LRU a logical break point for the network.

These and other aspects of the invention will be better understood whentaken in conjunction with the detailed description of the preferredembodiment and the drawings that are briefly described below. Of course,the invention is defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a known dedicated fiber dedicated fiber optic systemarchitecture

FIG. 2 shows a known serial networking dedicated fiber optic systemarchitecture.

FIG. 3 shows a serial networking dedicated fiber optic systemarchitecture in which the present invention may be operative.

FIG. 4 shows network configuration packets transmitted in a serialnetworking dedicated fiber optic system in some embodiments of theinvention.

FIG. 5 shows a LRU presence packet generation flow in some embodimentsof the invention.

FIG. 6 shows a HE-LRU hops packet generation flow in some embodiments ofthe invention.

FIG. 7 shows a method performed by a SN-LRU packet handler in someembodiments of the invention.

FIG. 8 shows a method performed by SN-LRU decision logic in someembodiments of the invention.

FIG. 9 shows a method performed by a HE-LRU packet handler in someembodiments of the invention.

FIG. 10 shows a method performed by HE-LRU decision logic in someembodiments of the invention.

FIGS. 11A and 11B show a method performed by SN-LRU decision logic insome embodiments of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 3 shows a serial networking dedicated fiber optic systemarchitecture in which the present invention may be operative. Thearchitecture includes HE-LRUs 300, which may be head end servers, andSN-LRUs 310, which may be seat VDUs. Each HE-LRU has at least two HE-LRUports 304 that each connect to an adjacent HE-LRU and zero or moreSN-LRU ports 305 that each connect to an adjacent SN-LRU. Each of theHE-LRU ports 304, 305 can be communicatively coupled with a processor onthe HE-LRU (e.g. processor 302). Each SN-LRU has at least two ports 308,309 that can each connect to an adjacent HE-LRU or SN-LRU. The ports308, 309 can be communicatively coupled with a processor on the SN-LRU(e.g. processor 312). Moreover, each HE-LRU and SN-LRU can have atopology database, such as a forwarding table that associates mediaaccess control (MAC) addresses of other LRUs with output ports of theHE-LRU or SN-LRU. The topology database in each HE-LRU and SN-LRU can becommunicatively coupled with the processor on the HE-LRU or SN-LRU.

In the architecture illustrated, a HE-LRUs 300 is connected to SN-LRUsat the edge of a serial chain of SN-LRUs 310 over a bidirectional link,e.g. fiber optics. Generally, the edge SN-LRUs connect back to differentHE-LRUs 300. At the head end, HE-LRUs 300 are connected to adjacentHE-LRUs over bidirectional links to form a ring of HE-LRUs. At the seatend, SN-LRUs 310 are connected to adjacent SN-LRUs over bidirectionallinks to form a serial chain of SN-LRUs. The system can employ most anytype of bidirectional link, such as fiber optics, copper wire, coaxialcable, wireless communication, or the like. In several embodiments,fiber optic links are employed to, among other advantages, increase datatransfer rate and/or capacity.

Network configuration protocols described herein are generally run tocreate and maintain a loop-free network topology on top of thearchitecture through selective transmission and processing ofconfiguration packets and selective blocking and unblocking of HE-LRUand SN-LRU ports.

FIG. 4 shows some of the types of network configuration packetstransmitted in a serial networking dedicated fiber optic system in someembodiments of the invention. Network configuration packets may passthrough both blocked and unblocked HE-LRU and SN-LRU ports, whereas datapackets (e.g. entertainment packets) may pass through unblocked portsbut may not pass through blocked ports.

A LRU presence packet 400 contains a packet type identifier indicatingthat packet 400 is a LRU presence packet. Packet 400 is used by a LRU todetermine whether a port is connected to a live LRU.

A HE-LRU hops packet 410 contains at least three fields. A first fieldis a packet type identifier indicating that packet 410 is a HE-LRU hopspacket. A second field is an identifier uniquely associated with theHE-LRU that originated packet 410. This field is used by a HE-LRU todetermine whether a received packet was originated by the HE-LRU itself(i.e. whether the packet has looped-back). A third field is a hops tohead end (HHE) value that is used to track the number of LRU hops packet410 has completed over a serial network chain.

A SN-LRU topology change packet 420 contains a packet type identifierindicating that packet 420 is a SN-LRU topology change packet. Packet420 is transmitted over a serial network chain and each SN-LRU thatreceives packet 420 clears its topology database and forwards packet 420along the chain. HE-LRUs convert received SN-LRU topology change packetsinto HE-LRU topology change packets that are circulated at the head endof the system.

A HE-LRU topology change packet 430 contains at least two fields. Afirst field is a packet type identifier indicating that packet 430 is aHE-LRU topology change packet. A second field is an identifier uniquelyassociated with the HE-LRU that originated packet 430. Packet 430 iscirculated at the head end of the system in response to a detectedtopology change. In some embodiments, each HE-LRU that receives packet430 clears its topology database.

FIG. 5 shows a LRU presence packet generation flow in some embodimentsof the invention. After startup (500), an originating LRU (e.g. HE-LRUand/or SN-LRU) under local processor control generates and sends a LRUpresence packet out all the originating LRU's ports (510). Theoriginating LRU delays for a period of time equal to the inverse of aconfigured refresh rate for the presence packet (520) after which itrepeats the process in loop. In some embodiments, each HE-LRU and SN-LRUinclude a processor and execute this presence packet generation flowmethod under local processor control.

FIG. 6 shows a HE-LRU hops packet generation flow in some embodiments ofthe invention. After startup (600), an originating HE-LRU under localprocessor control generates and sends a HE-LRU hops packet out all theoriginating HE-LRU's ports (610). The originating HE-LRU delays for aperiod of time equal to the inverse of a configured refresh rate for theHE-LRU hops packet (620) after which it repeats the process in loop. Insome embodiments, each HE-LRU executes this hops packet generation flowmethod under local processor control.

FIG. 7 shows a method performed by a SN-LRU packet handler in someembodiments of the invention. Upon reception of a management packet, apacket handler executed by a processor on the SN-LRU determines thepacket type by inspecting the packet type identifier field in the packet(700). In some arrangements, the packet handler processes three packettypes: LRU presence packet, HE-LRU hops packet, and SN-LRU topologychange packet. If the packet is a LRU presence packet, the packethandler sets a current state variable of the ingress port (i.e. the porton which the packet was received) to active (710). The current statevariable informs decision logic executed by the processor that theingress port is connected to a live LRU. If the packet is a HE-LRU hopspacket, the packet handler increments the HHE value in the packet, setsthe ingress port HHE count to the HHE value in the packet, and forwardsthe updated HE-LRU hops packet to the non-ingress port (720). If thepacket is a SN-LRU topology change packet, the packet handler clears thetopology database on the SN-LRU and forwards the packet out thenon-ingress port (730).

FIG. 8 shows a method performed by SN-LRU decision logic in someembodiments of the invention. After startup (800), logic executed by aprocessor on the SN-LRU blocks both ports of the SN-LRU and sets a laststate variable of both ports to blocked (810). The flow then proceeds tothe main processing loop. At the start of each pass through the mainprocessing loop, the logic sets a current state variable of both portsto inactive and sets the HHE count for both ports to zero (820). Thelogic then delays for a period greater than the presence loop and hoploop periods to afford the packet handler ample time to perform thesteps shown in FIG. 7 on packets generated in accordance with FIGS. 5and 6, which updates port state variables and HHE count based on thecurrent network topology. After the delay, the logic determines whetherthe serial network chain of which the SN-LRU is a part is closed or openby inspecting the HHE count for both ports. If either count is zero,then the network is open (i.e. paths do not exist in both directions toa HE-LRU). If both counts are non-zero, the network is closed (i.e.paths exist in both directions to a HE-LRU) (830).

If the network is closed, the flow proceeds to Step 840 where the logicfirst determines whether the SN-LRU on which the logic is operative is amiddle LRU of a serial network chain. This is determined by comparingthe HHE count for both ports. If the HHE count for both ports is thesame or differs by only one hop, the SN-LRU is a middle LRU; otherwise,the SN-LRU is not a middle LRU. If the SN-LRU is a middle LRU, theSN-LRU has responsibility to break the chain and create a loop-freenetwork topology. In that event, the logic blocks the port with thehigher HHE count (i.e. longer path to the head end) and unblocks theother port. If the HHE count for both ports is identical, the logicblocks a predetermined at least one of the ports and unblocks the otherport. The logic next determines whether the last state variable of theblocked port is unblocked. If the last state variable of the blockedport is unblocked, the network topology changed in a way that put theSN-LRU at the end of a chain and thus the SN-LRU should inform thesystem of the topology change. Accordingly, the logic clears thetopology database and generates and transmits on the unblocked port aSN-LRU topology change packet, forcing relearning of the networktopology. The logic next sets the last state variable of the blockedport to blocked, and sets the last state variable of the unblocked portto unblocked. If the SN-LRU determines it is not a middle LRU, the logicunblocks both ports and sets the last state variable of both ports tounblocked.

If the network is open, the flow proceeds to Step 850 where the logicdetermines for each port whether the current state variable is active orinactive and takes appropriate action. If the current state variable isactive, the logic unblocks the port and sets the last state variable tounblocked. If the current state variable is inactive, the logic blocksthe port and, if the last state variable is unblocked, clears thetopology database and transmits a SN-LRU topology change packet on theunblocked port, forcing relearning of the network topology. Finally, thelogic sets the last state variable to blocked.

FIG. 9 shows a method performed by a HE-LRU packet handler in someembodiments of the invention. Upon reception of a management packet, apacket handler executed by a processor on the HE-LRU determines thepacket type by inspecting the packet type identifier field in the packet(900). In the embodiment shown, the HE-LRU packet handler processes fourpacket types: LRU presence packet, HE-LRU hops packet, SN-LRU topologychange packet, and HE-LRU topology change packet. If the packet is a LRUpresence packet, the packet handler sets the current state variable ofthe ingress port to active (910). The current state variable generallyinforms decision logic executed by the processor that the ingress portis connected to a live LRU. If the packet is a HE-LRU hops packet, thepacket handler first determines whether the ingress port is a SN-LRUport and, if so, discards the packet. The packet handler then determinesif the packet was originated by the HE-LRU itself (i.e. whether thepacket has looped-back). If the HE-LRU is the originating HE-LRU forthis packet, the network is closed and the packet handler sets a networkstate variable to closed and discards the packet. If, on the other hand,the HE-LRU is not the originating HE-LRU for this packet, the packethandler forwards the packet on the non-ingress HE-LRU port (920). Uponreception of a SN-LRU topology change packet, the packet handler clearsthe topology database and transmits a HE-LRU topology change packet onboth HE-LRU ports to inform other HE-LRUs of the topology change (930).Upon reception of a HE-LRU topology change packet, the packet handlerfirst determines if the packet was originated by the HE-LRU itself (i.e.whether the packet has looped-back). If the HE-LRU is the originatingHE-LRU for this packet, the packet handler discards the packet;otherwise, the packet handler clears the topology database and forwardsthe packet to the non-ingress HE-LRU port (940).

FIG. 10 shows a method performed by HE-LRU decision logic in someembodiments of the invention. After startup (1000), logic executed by aprocessor on the HE-LRU generally blocks both HE-LRU ports, unblocks allSN-LRU ports, and sets a last state variable of both HE-LRU ports toblocked (1010). The flow then proceeds to the main processing loop. Atthe start of each pass through the main processing loop, the logic setsa current state variable of both HE-LRU ports to inactive and sets thenetwork state variable to open (1020). The logic then delays for aperiod greater than the presence loop and hop loop periods to afford thepacket handler ample time to perform the steps shown in FIG. 9 whichupdates port state variables and the network state variable based on thecurrent network topology. After the delay, the logic determines whetherthe head end ring network of which the HE-LRU is a part is closed oropen by reference to the network state variable (1030).

If the network is closed, the logic at Step 1040 first determineswhether the HE-LRU on which the logic is operative has been designatedto break the loop. This is determined by referencing a unique break LRUidentifier available to the HE-LRU. If the HE-LRU is the designatedbreak LRU, the HE-LRU has responsibility to break the ring and create aloop-free head end network topology. In that event, the logic blocks apredetermined at least one of the HE-LRU ports and unblocks the otherHE-LRU port. The logic next determines whether the last state variableof the blocked port is unblocked. If the last state variable of theblocked port is unblocked, the HE-LRU should inform the system of thetopology change. Accordingly, the logic clears the topology database andgenerates and transmits a HE-LRU topology change packet on the unblockedHE-LRU port, forcing relearning of the network topology. The logic nextsets the last state variable of the blocked HE-LRU port to blocked, andsets the last state variable of the unblocked HE-LRU port to unblocked.If the HE-LRU determines it is not the designated break LRU, the logicunblocks both HE-LRU ports and sets the last state variable of bothHE-LRU ports to unblocked.

If the network is open, the logic at Step 1050 determines for eachHE-LRU port whether the current state variable is active or inactive andtakes appropriate action. If the current state variable is active, thelogic unblocks the port and sets the last state variable to unblocked.If the current state variable is inactive, the logic blocks the portand, if the last state variable is unblocked, clears the topologydatabase and transmits a HE-LRU networking topology change packet on theunblocked port, forcing relearning of the network topology. Finally, thelogic sets the last state variable to blocked.

FIGS. 11A and 11B show a method performed by SN-LRU decision logic insome embodiments of the invention. In these embodiments, after an SN-LRUchain recovers from a fault, the break point in an SN-LRU chain ismaintained at the initial break point rather than reverting to themiddle of the SN-LRU chain. The initial break point is kept in theseembodiments to avoid “ping ponging” between the initial break point anda break point at the middle of the SN-LRU chain when failure at theinitial break point is a recurring problem. As shown in FIG. 4, in theseembodiments historical break information is shared between SN-LRUs usinga logical break port identifier that is carried in HE-LRU hops packets410, as will be explained now in greater detail.

Referring to Step 720 of FIG. 7, an SN-LRU that has detected a physicalbreak at one of its ports applies to an HE-LRU hops packet that itreceives on its ingress port a logical break port identifier identifyingits physical break port before forwarding the HE-LRU hops packet on itsnon-ingress port, replacing any logical break port identifier containedin the packet as received. SN-LRUs in an SN-LRU chain reference thelogical break port identifiers (or absence thereof) in received HE-LRUpackets to identify an appropriate physical break point for the chain,as will now be explained in conjunction with FIGS. 11A and 11B.

After startup (1100), logic executed by a processor on the SN-LRU blocksboth ports of the SN-LRU, sets a last state variable of both ports toblocked, and sets its logical break port identifier to undefined (1110).The flow then proceeds to the main processing loop. At the start of eachpass through the main processing loop, the logic sets a current statevariable of both ports to inactive and sets the HHE count for both portsto zero (1120). The logic then delays for a period greater than thepresence loop and hop loop periods to afford the packet handler ampletime to perform the steps shown in FIG. 7 on packets generated inaccordance with FIGS. 5 and 6, which updates port state variables andHHE count based on the current network topology. After the delay, thelogic determines whether the serial network chain of which the SN-LRU isa part is closed or open by inspecting the HHE count for both ports. Ifeither count is zero, then the network is open (i.e. paths do not existin both directions to a HE-LRU). If both counts are non-zero, thenetwork is closed (i.e. paths exist in both directions to a HE-LRU)(1130).

If the network is closed, the flow proceeds to Step 1140 where the logicfirst determines whether a logical break port exists in the network as aresult of a previous failure from which recovery has been made. Ifeither of the ports on the SN-LRU on which the logic is operative is alogical break port (due to a previous physical break at that port) andno other logical break port exists in the network, the flow returns toStep 1120 without further action, resulting in a blocked port on theSN-LRU remaining blocked.

If either of the ports on the SN-LRU on which the logic is operative isa logical break port and another logical break port exists in thenetwork, a further check is made to determine which of the logical breakports is closer to the middle of the SN-LRU chain, which can bedetermined by reference to HHE counts. In that event, if the logicalbreak port on the SN-LRU on which the logic is operative is closer tothe middle, or is the same distance from the middle and indicated to winin the event of a tie, the flow returns to Step 1120 without furtheraction, resulting in a blocked port on the SN-LRU remaining blocked. Onthe other hand, if the logical break port on the SN-LRU on which thelogic is operative is further from the middle, or is the same distancefrom the middle and indicated to lose in the event of a tie, the logicunblocks both of the ports on the SN-LRU.

In some embodiments, if neither of the ports on the SN-LRU on which thelogic is operative is a logical break port and another logical breakport exists in the network, the logic unblocks both of the ports on theSN-LRU.

In certain arrangements, if neither of the ports on the SN-LRU on whichthe logic is operative is a logical break port and no other logicalbreak port exists in the network, the SN-LRU on which the logic isoperative determines if it is a middle LRU of a serial network chain.This is determined by comparing the HHE count for both ports. If the HHEcount for both ports is the same or differs by only one hop, the SN-LRUis a middle LRU; otherwise, the SN-LRU is not a middle LRU. If theSN-LRU is a middle LRU, the logic blocks the port with the higher HHEcount (i.e. longer path to the head end) and unblocks the other port. Ifthe HHE count for both ports is identical, the logic blocks apredetermined at least one of the ports and unblocks at least one otherport. If the SN-LRU determines it is not a middle LRU, the logicunblocks both ports.

Generally, if the last state variable of any blocked port was unblocked,the logic clears the topology database and generates and transmits onthe unblocked port a SN-LRU topology change packet, forcing relearningof the network topology. The logic also sets the last state variable ofany blocked port to blocked, and sets the last state variable ofunblocked ports to unblocked.

If the network is open, the flow proceeds to Step 1150 where the logicdetermines for each port whether the current state variable is active orinactive and takes appropriate action. If the current state variable isactive, the logic unblocks the port and sets the last state variable tounblocked. If the current state variable is inactive, the logic sets thelogical break port identifier to the current port, blocks the port and,if the last state variable is unblocked, clears the topology databaseand transmits a SN-LRU topology change packet on the unblocked port,forcing relearning of the network topology. Finally, the logic sets thelast state variable to blocked.

It will be appreciated by those of ordinary skill in the art that theinvention can be embodied in other specific forms without departing fromthe spirit or essential character hereof. The present description istherefore considered in all respects to be illustrative and notrestrictive. The scope of the invention is indicated by the appendedclaims, and all changes that come with in the meaning and range ofequivalents thereof are intended to be embraced therein.

The following is claimed:
 1. An in-flight entertainment (IFE) systemcomprising: a plurality of serial networking line replaceable units(SN-LRUs); and a plurality of head end line replaceable units (HE-LRUs)in communication with the SN-LRUs, at least one of the plurality ofHE-LRUs being a blocking HE-LRU, the blocking HE-LRU comprising: aprocessor; and a plurality of ports communicatively coupled with theprocessor, the plurality of ports comprising a first port and a secondport, the blocking HE-LRU configured to transmit a packet on at leastthe first port and to determine whether the packet has been received onthe second port; the blocking HE-LRU in communication with a databasecomprising unique identifiers for each of the plurality of HE-LRUs, theblocking HE-LRU configured to determine whether the unique identifierfor the blocking HE-LRU is designated as a break line replaceable unit(LRU); wherein, under control of the processor, the blocking HE-LRU isconfigured to block one of the first and second ports in response todetermining that a condition is satisfied, the condition comprising: thepacket transmitted on the first port has been received on the secondport; and the unique identifier for the blocking HE-LRU is designated asthe break line replaceable unit (LRU).
 2. The IFE system of claim 1,wherein, in response to determining that the condition is satisfied, theblocking HE-LRU is further configured to clear a topology database onthe blocking HE-LRU.
 3. The IFE system of claim 2, wherein under controlof the processor, the blocking HE-LRU is further configured to transmita topology change packet, via an unblocked one of the first and secondports, to at least one other of the plurality of HE-LRUs.
 4. The IFEsystem of claim 1, wherein, in response to determining that thecondition is satisfied, the HE-LRU is further configured to unblock theother of the first and second ports.
 5. The IFE system of claim 4,wherein: the blocking HE-LRU further comprises a last state variable forthe first port and a last state variable for the second port; and inresponse to determining that the condition is satisfied, the blockingHE-LRU is further configured to: determine whether the last statevariable of the blocked port indicates blocked or unblocked; and inresponse to determining that the last state variable of the blocked portindicates unblocked, to transmit a topology change packet on theunblocked port.
 6. The IFE system of claim 5, wherein, in response todetermining that the condition is satisfied, the blocking HE-LRU isfurther configured to: set the last state variable of the blocked portto blocked; and set the last state variable of the unblocked port tounblocked.
 7. The IFE system of claim 1, wherein, in response todetermining that the unique identifier for the blocking HE-LRU is notdesignated as the break LRU, the blocking HE-LRU is further configuredto: unblock the first port; set a last state variable of the first portto unblocked; unblock the second port; and set a last state variable forthe second port to unblocked.
 8. The IFE system of claim 1, wherein theblocking HE-LRU comprises a server.
 9. The IFE system of claim 1,wherein the plurality of SN-LRUs comprise video display units.
 10. TheIFE system of claim 9, wherein each of the plurality of SN-LRUs areconfigured to individually determine whether a closed communicationnetwork has been formed between the plurality of HE-LRUs and theplurality of SN-LRUs, such determination being at least partially basedon a plurality of packets sent from at least one of the HE-LRUs andreceived on a plurality of ports of each of the SN-LRUs.
 11. The IFEsystem of claim 10, wherein one of the plurality of SN-LRUs isconfigured to block one of its ports in response to detecting that anSN-LRU condition is satisfied, the SN-LRU condition comprising: theclosed communication network has been formed between the plurality ofHE-LRUs and the plurality of SN-LRUs; and the one of the plurality ofSN-LRUs comprises a middle SN-LRU.
 12. A method of operating anin-flight entertainment (IFE) system comprising a plurality of serialnetworking line replaceable units (SN-LRUs) and a plurality of head endline replaceable units (HE-LRUs), at least one of the plurality ofHE-LRUs being a blocking HE-LRU, the method comprising: determining,with the blocking HE-LRU, that a closed HE-LRU network exists, whereindetermining that a closed HE-LRU network exists comprises: transmittinga packet on a first port of the blocking HE-LRU; and receiving thepacket on a second port of the blocking HE-LRU; determining, with theblocking HE-LRU, that the blocking HE-LRU is designated as a break LRU,wherein determining that the blocking HE-LRU is designated as the breakLRU comprises: referencing a unique break LRU identifier; anddetermining whether the unique break LRU identifier identifies theblocking HE-LRU as the designated break line replaceable unit (LRU); andin response to determining that the closed HE-LRU network exists andthat the blocking HE-LRU is designated as the break LRU: blocking one ofthe first and second ports of the blocking HE-LRU, thereby creating aloop-free HE-LRU network topology.
 13. The method of claim 12, furthercomprising: in response to determining that the closed HE-LRU networkexists and that the blocking HE-LRU is designated as the break LRU:unblocking the other of the first and second ports of the blockingHE-LRU.
 14. The method of claim 12, further comprising: determiningwhether a last state variable of the blocked port indicates blocked orunblocked; and in response to determining that the last state variableof the blocked port indicates unblocked, informing another of theplurality of HE-LRUs of a topology change.
 15. The method of claim 14,wherein informing another of the plurality of HE-LRUs of a topologychange comprises: transmitting a topology change packet on the unblockedport of the blocking HE-LRU.
 16. The method of claim 15, furthercomprising clearing the topology database on each of the plurality ofHE-LRUs.
 17. The method of claim 16, further comprising: setting thelast state variable of the blocked port to indicate blocked; and settinga last state variable of the unblocked port to indicate unblocked. 18.The method of claim 12, further comprising: in response to determiningthat the blocking HE-LRU is not designated as the break LRU: unblockingthe first port; setting a last state variable of the first port toindicate unblocked; unblocking the second port; and setting a last statevariable for the second port to indicate unblocked.
 19. An in-flightentertainment (IFE) system comprising: a plurality of serial networkingline replaceable units (SN-LRUs); and a plurality of head end linereplaceable units (HE-LRU), at least one of which comprises: aprocessor; and a plurality of ports communicatively coupled with theprocessor, the HE-LRU configured to transmit a packet on at least one ofthe plurality of ports; wherein, under control of the processor, the atleast one HE-LRU is configured to block one of its ports in response to:detecting that a packet transmitted on a first one of the at least oneHE-LRU's ports has been received on a second one of the at least oneHE-LRU's ports; and detecting that the HE-LRU is a designated break linereplaceable unit (LRU).
 20. The IFE system of claim 19, wherein theHE-LRU under control of the processor clears a topology database on theHE-LRU based on detecting that a packet transmitted on a first one ofthe ports has been received on a second one of the ports and based onfurther detecting that the HE-LRU is a designated break LRU.
 21. The IFEsystem of claim 19, wherein the HE-LRU under control of the processortransmits a topology change packet on an unblocked one of the portsbased on detecting that a packet transmitted on a first one of the portshas been received on a second one of the ports and based on furtherdetecting that the HE-LRU is a designated break LRU.
 22. The IFE systemof claim 19, wherein the HE-LRU comprises a server.